1. Impression Evidence
Glatt

2. What is impression evidence?
Impression evidence- can be defined as objects or materials that have retained the characteristics of other objects through direct contact.
Impressions are created when one object is pressed against another material with enough force to leave an impression of the object. 
Shoeprints, tool marks, tire tracks, bite marks, and marks on a fired bullet are several examples of impression evidence.
Impressions may be found in or on many different types of materials. The quality of the impression depends on the object making the impression and the surface conditions, such as how hard or soft it is and what type of material it is (soil, mud, dust, concrete, grass, skin, etc.)
CSI & Impressions
Images: and

3. Types of Impressions
Patent impressions- are visible, two-dimensional impressions produced as an object moves through soil, dust, paint, blood, or other fine particles and leaves a trace
Latent impressions- are hidden impressions (made by oils, fine soil and other minute debris) that can be obtained with special techniques
special dusting and electrostatic techniques
Chemical developers
Plastic impressions- are 3-dimensional imprints. These impressions can be left in soft materials such as snow, mud, soil ect…

4. Individual or Class Evidence
Depending on how they are made, impressions may be either class evidence or individual evidence
A particular tread pattern in shoes or in tires may identify the brand and size, but does not identify a specific individual
Distinguishing characteristics, such as cut or nick on a shoe sole or unusual wear on a car tire, can make impressions very distinctive and can be used as individual evidence

5. Shoe Impressions Shoe Wear Patterns
Although two different people may purchase the same type of shoes, the wear pattern on the shoes can appear quite different and can individualize the impression evidence.
Some factors that can personalize our footwear include:
The size of the foot and the wearer’s activities
Size of foot also correlated with person’s height
Body weight
Depth of impression
Pigeon toed or duck footed or straight
Whether a person walks on their toes or heels
The surface on which the person normally walks
Unique holes, cuts, or debris that may become embedded in the shoe
The type of shoe can tell something of the person’s job or personality

6. Shoe Impressions Gait and Tracks
Numerous prints together tell an investigator about the person’s gait, or walking habit
Limp or injury = assymetrical gait
One foot angle differently than other
Also may be a sign that person was carrying heavy weight
Walking or running
Trail of prints may also provide the movements of individuals at a crime scene
Reconstruct events
Occurrences or what happened
Entrance and exit to crime scene
Number of people at the crime scene

7. Collection of Shoe Impression Evidence Photographing Impressions
Guidelines for Photographing Impressions
Take photos before anyone touches or alters impression
Fill cameras viewfinder with the impression for close ups
Multiple photographs at different angles
Identifying label and ruler included in picture
Shaded or indirect lighting to avoid glare
Photograph relationship of impression to the whole crime scene
Patent prints will only be photographed, latent prints will be photographed and can be lifted (sometimes), plastic prints will be photographed cast

8. Lifting Latent Prints Latent = invisible to naked eye
Luminol to make bloody footprints visible and able to be photographed
Dusting of the latent print, similar to dusting for fingerprints, to reveal an impression and make it visible to be photographed and lifted
Electrostatic lifting and gel lifting techniques to capture invisible impressions
Electrostatic lifting- electrostatic charge applied to lifting film and then placed over latent print
Fine dust can be detected
Paper, flooring including carpet, wood, linoleum, asphalt
Gel Lifting
Best on oily or moist prints
Print is first dusted with powder, gel templated with cardboard backing is then used to lift print

9. Casting Plastic Prints
Plastic or 3-Dimensional impressions are cast, after photographing, to preserve the physical evidence
Casting materials and techniques vary with the conditions of the crime scene
Sand/dirt- Plaster of Paris
Light layer of hair spray deposited first to avoid collapse of the print due to weight of the plaster of paris
Snow- spray wax applied first and instantly freezes to preserve border of imprint, then dental stone used to cast impression

10. Height vs Shoe Size
Direct relationship between a person’s height and shoe size
Increase shoe size equals increased height
Height of suspect can be estimated
Some margin of error

12. Tire Treads and Impressions
Motor vehicles can leave patent, latent, and plastic impressions.
Treated much the same as shoeprints
Class characteristics involve design, size, type, and model.
Wear and damage cause defects that can lead to individualization
Tire evidence can be used to link a suspect to a crime scene
Tire pattern and measurements can be used to identify the type of tire and perhaps make and model of car
A large database contains track width, wheelbase, and turning diameter measurements for all makes and models of vehicles
Can be easily checked to identify the vehicle that left impressions
Tire evidence can reveal events that took place
Nature of Impression can be used to determine how the vehicle was driven
Tire marks may indicate speed at which a car was traveling
Skids marks at an accident may be used to determine who was at fault

13. Tread Impressions Tread Pattern
Ridges (raised sections) and Grooves can be counted and measured for identification of Brand of Tire
Ribs (raised section) can be odd or even
Width of ribs and grooves differs from tire to tire
Sipes and tread blocks also leave unique tread pattern/impression
Imperfections such as wear patterns or embedded pebbles can individualize tire evidence

14. Identifying a Vehicle Wheel Base and Track Width
Wheel Base and Track Width Measurements may help identify make and model
Wheel Base- is the distance from the center of the front axle to the center of the rear axle
Track Width- is the distance from the center of a tire on the passenger side of vehicle to the center of a tire on the driver side of the vehicle
The front and rear track width measurements may differ

15. Measuring Track Width

16. Identifying a Vehicle Turning Diameter
Also commonly known as turning radius
Imprint Seen when cars make U turns
How tight a circle can be driven by vehicle?
Longer wheel base equals a longer turning diameter

18. Accident Reconstruction
Skid Marks
Formed when someone breaks suddenly and lock the brakes
Provides evidence of the distance brakes were applied
Calculation of velocity (speed) can be made from skid marks
Tires melt on road due to extreme temps caused by friction, audible squeal and often smoke occurs
Yaw Marks
Produced when vehicle travels in a curved path faster than the vehicle can hand and skids
Tire Scrub
Produced by overloaded or damaged tire during or immediately after impact
Usually curved, irregular in width
Determines area of impact

19. Dental Impressions
Dental Impressions, like fingerprints, are generally considered to be individual evidence
Factors leading to individuality of teeth
Number of teeth/Missing teeth
Coloration of teeth
Size of teeth
Alignment of teeth and distance between teeth
Unique fillings, crowns, caps
Overall condition of teeth (breakage/chipped teeth, grinded teeth ect…)

20. Dental Impressions/Evidence
Can be used to identify remains of deceased
Can be used in profiling and identifying a suspect from unique patterns or bite marks left at the scene of a crime

22. Age Determination
Number and type of adult/baby teeth present can be used to approximate age in children x

23. Dental Impressions 32 total teeth (***including 4 wisdom teeth)
16 teeth on top and bottom in adults
Central incisors (2) – front, cutting
Lateral incisors(2) – both sides of central incisors, cutting
Canines (2) – cutting and tearing
First premolar (2) - hybrid
Second premolar (2) - hybrid
First molar (2) – chewing and grinding
Second molar (2) – chewing and grinding
3rd molar, wisdom teeth (2)- ***can be variable, not everyone has them
Genetics
Surgical Removal

24. Bite Mark Comparisons Up to 76 points of comparison
Places where locations on bite where impressions are often detailed
Comparison includes:
Dental chipping, surface indentations, distances between teeth, alignment of teeth, angle of mouth arch, absence of teeth
Bite mark should be photographed with ruler included as soon as possible
Bite mark should be swabbed, may contain DNA from saliva

25. Famous Cases Ted Bundy OJ Simpson (Simpson-Goldman Murders )
Serial killer who killed over an estimated 50 women
Bite marks obtained from Florida State University sorority attack
4 attacked, 2 killed
Escaped from police twice, bite mark evidence led to conviction
Executed in 1989
OJ Simpson (Simpson-Goldman Murders )
Bloody shoe print (patent) left at crime scene
Shoe never found
OJ Verdict not guilty in criminal trial
Found liable of wrongful death in civil suit after pictures surfaced of OJ wearing the exact type of shoe that made imprint (ALONG with ALOT of other EVIDENCE)